Thursday, February 13, 2014

Yellow-eyed penguins forage in trawlers' wake

New Zealand's endangered yellow-eyed penguin have been found to
follow the line of swooping seabirds - literally - when it comes to
reaping the food stirred up by trawlers.

An Otago University
research team have discovered the penguins, of which there were around
500 estimated pairs left on mainland New Zealand, forage in straight
lines for several kilometres by following furrows in the seafloor
scoured out by fishing trawlers.

Using GPS dive loggers the
researchers monitored the penguins' movements over three years showing
the birds use furrows scoured on the seabed by otter boards from trawl
nets to find food, particularly blue cod. "This research is
unique as it shows for the first time that not only do flying seabirds
follow fishing vessels, but also penguins, with the latter foraging
after a trawler has gone through a particular area," lead research
Professor Philip Seddon said.

The researchers said blue cod and
other bottom feeders were likely to forage around the seafloor lines
because they were attracted to the marine life stirred up and exposed by
the action of the nets being dragged behind fishing trawlers. The
lines made by the otter boards, which keep the mouth of the trawl net
open, are up to 15cms wide and two centimetres in depth on a north-east
to south-west axis.

They can remain on the sea floor for a year or more and are clearly visible. GPS
dive loggers were attached to the back of the birds to determine the
depth the penguins dive, their locations and line of travel and how far
they swim in one foraging trip. Lines on the seafloor were
located by using video footage taken by a remote operated vehicle
launched from the university's research vessel Polaris II.

Many
penguins swim to a depth of between 60 and 70 metres to feed during
multiple dives - up to 80 - over several hours before returning to
shore. The penguins can travel up to 120 kilometres in one trip,
while foraging in the mid-shelf fishing grounds some 20 kilometres off
the Otago Peninsula.

The study shows that the birds also revisit
the lines on subsequent occasions and might develop a visual memory of
the area, researchers say. "It appears that using the lines for
foraging is particularly related to bad breeding years when penguins are
more likely to go further out to sea to find blue cod and other bottom
feeders. This might also be due to the individual preference of some
birds though," said Dr Thomas Mattern, the first author of the paper
reporting the results. But the researchers say that one of the
downsides of foraging around the trawl lines might be that an exclusive
diet of blue cod, which tends to be low in nutritional value, could
affect breeding.

As yet, there was no confirmation of this
hypothesis and further research was needed to determine if there is any
relationship between foraging patterns, diet quality and breeding
success in the penguin population.

The research was published in the journal PloS ONE and supported by the Yellow-Eyed Penguin Trust.